1. Field of the Invention
The present invention relates to a blood pressure cuff for a sphygmomanometer that is used by being attached to some region of a living body or subject for measuring blood pressure. In particular, the invention relates to a cuff most appropriate for a wrist sphygmomanometer for measuring blood pressure at the wrist portion.
2. Description of the Background Art
FIGS. 9A and 9B illustrate a conventional sphygmomanometer cuff. As shown in FIGS. 9A and 9B, the conventional sphygmomanometer cuff 70 is constituted of an air bag 71 into which air is supplied and a strip-like band 72 for attaching air bag 71 to a certain region (arm, wrist) 80 of a living body or subject. Band 72 of cuff 70 is used to attach air bag 71 to subject region 80 and then air is supplied to air bag 71, so that an artery 81 of subject region 80 is pressurized and accordingly blood pressure is measured during the process of discharging air from air bag 71.
Japanese Patent Publication No. 6-28636 (Japanese Patent Laying-Open No. 63-147434) discloses xe2x80x9cSphygmomanometer Arm Band and Sphygmomanometer Pressurizing Devicexe2x80x9d as a prior art of the sphygmomanometer cuff. The sphygmomanometer arm band includes, in addition to a main body of the arm band, an inflatable bag and connecting means, an actuator for decreasing the diameter of the arm band by shortening the length of the arm band body. Regarding this arm band, the actuator is inflated before expansion of the inflatable bag and thus the arm band body is tighten up to an extent which is sufficient to measure blood pressure. The inflatable bag is thereafter distended to have a pressure sufficiently higher than the maximum blood pressure and then the air within the inflatable bag is gradually discharged. Blood pressure is thus measured during the discharging process.
In conventional cuff 70, the pressurizing force required to block the flow of blood in artery 81 is provided by the volume of expansion of air bag 71 only. If cuff 70 is closely attached to subject region 80 as shown in FIG. 9A, air bag 71 has a wide flat portion (effective range). When air bag 71 is distended in this state, the pressurizing force is conveyed to artery 81 which is enough to block the flow of blood in artery 81. On the other hand, if cuff 70 is attached loosely to subject region 80 as shown in FIG. 9B, air bag 71 has a relatively narrow effective range. Therefore, even if air bag 71 is inflated sufficiently in this state, the pressurizing force is not conveyed to artery 81 and accordingly the flow of blood in artery 81 is not blocked. In this case, an additional volume of expansion of air bag 71 is required corresponding to the space between air bag 71 and the skin, resulting in a measurement higher than a true value.
In order to avoid this problem, cuff 70 should be closely fit onto subject region 80 as shown in FIG. 9A. However, if cuff 70 stands being attached closely to subject region 80 all the time, there would arise a feeling of being excessively pressurized. Especially in the period of sweaty summer or rainy season, there would arise discomfort. The resultant problem is difficulty in constant attachment of the sphygmomanometer (particularly wrist sphygmomanometer) even if the sphygmomanometer body or cuff is reduced in size.
Regarding the arm band and pressurizing device disclosed in the patent above, the actuator operates to reduce the diameter of the arm band and the arm band is then closely attached to the subject in a manner similar to the conventional wrapping state, and the operation of the actuator is cancelled to allow the diameter of the arm band to increase and thus loosen the arm band. This approach advantageously achieves the effect of avoiding the discomfort caused by the feeling of being excessively pressurized and unpleasant dampness. However, in measurement of blood pressure, the actuator is first expanded to pull and accordingly tighten the arm band body and then the inflatable bag is distended until a predetermined pressure is obtained. Therefore, the inflatable bag is likely to be shifted from its original position. In other words, the possibility of the shift of the inflatable bag is higher when the actuator operates to pull the arm band body after the arm band is loosely attached at first. In the event of the shift of the inflatable bag, a sufficient degree of pressurizing force cannot be conveyed to the artery, resulting in the state shown in FIG. 9B. If the blood flow in the artery is to be blocked in this state, the volume of expansion of the inflatable bag must be increased, causing further discomfort such as the feeling of excessive pressurization.
One object of the present invention is to provide a sphygmomanometer cuff which can ensure blocking of the blood flow in an artery so as to obtain measurements with higher precision.
Another object of the present invention is to provide a sphygmomanometer cuff capable of eliminating discomfort caused by the feeling of being excessively pressurized, dampness and the like.
Still another object of the present invention is to provide a sphygmomanometer cuff having a pressurization surface ensuring pressurization of a particular region of a living subject.
Those objects of the present invention can be accomplished by a sphygmomanometer cuff which includes the following components. Specifically, a sphygmomanometer cuff according to one aspect of the present invention includes a fluid bag for pressurization into or in which a predetermined amount of fluid is supplied or confined and to which a pressure sensor is connected, a press portion into which a predetermined amount of fluid is supplied to cause the pressurization fluid bag to press a region of a living subject, and an attachment unit for attaching the pressurization fluid bag and the press portion to the subject region.
The pressurization fluid bag of the cuff having the pressure sensor connected thereto is different from the conventional cuff and the inflatable bag disclosed in the patent above in that only a predetermined amount of fluid is supplied into the fluid bag or a predetermined amount of fluid is confined therein in advance and then the press portion causes the pressurization fluid bag to press the subject region. In measurement of blood pressure, the press portion may just be used to press the pressurization fluid bag against the subject region. Therefore, the cuff may be attached loosely to the subject region and accordingly the discomfort caused by the feeling of excess pressure and dampness can be avoided so as to enable the cuff to be attached all the time. Further, only a predetermined amount of fluid is supplied into or confined in the pressurization fluid bag, and the force for sufficiently pressurizing the subject region by the pressurization fluid bag is obtained by the press portion. Specifically, the press portion causes the pressurization fluid bag to press the subject region. By positioning the pressurization fluid bag at a predetermined site (where artery is pressurized) when the cuff is attached, even if the cuff is attached loosely, it is possible to prevent shift of the position of the pressurization fluid bag due to the operation of the press portion which hinders conveyance of a sufficient pressure to the artery. Measurements with higher precision can thus be obtained.
According to another aspect of the invention, a sphygmomanometer cuff includes a fluid bag for pressurization into or in which a predetermined amount of fluid is supplied or confined and which is connected to a pressure sensor, a press unit into which a predetermined amount of fluid is supplied for causing the pressurization fluid bag to press the subject region, and an attachment unit for attaching the pressurization fluid bag and the press unit to the subject region. The pressurization fluid bag is curved along the surface of the subject region. The pressurization fluid bag fits onto the surface of the subject region without gap, so that the pressure on the artery can correctly be detected and accordingly the blood pressure can be measured with high precision.
The pressurization fluid bag may be divided into small parts which are placed in the circumferential direction of the subject region. The pressurization fluid bag is thus composed of a plurality of small bags, not of one bag, so as to improve fitness onto the surface of the subject region and accordingly achieve correct measurement of the pressure on the artery.
The pressurization fluid bag may have a wavelike structure with projection and depression extending in the axial direction of the subject region. Even if the pressurization fluid bag is partially caught by tendon or bone in the subject region when the pressure is exerted, the wavelike structure allows the remaining part to move in the pressurized direction regardless of the caught portion, so that the pressure on the artery can correctly be detected.
The pressurization fluid bag may have a portion extending in the axial direction of the subject region that has a hardness different from that of the remaining portion. The portion of the pressurization fluid bag to be associated with the tendon and bone in the subject region may have a hardness lower than that of the remaining portion so that the portion associated with the tendon and bone is easily compressed and the remaining portion moves in the pressurized direction regardless thereof. In this way, the pressure on the artery can correctly be detected.
The pressurization fluid bag includes a pressurization surface which is more elastic than the subject region and includes a portion having a compression displacement relative to the pressure from the subject region smaller than compression displacement of fluid inside the pressurization surface. Here, the compression displacement means a displacement caused by compression due to the pressure from the subject region. When pressure is exerted, the pressurization surface is pushed by the subject region to be displaced inwardly, while the remaining portion is hardly displaced. Consequently, the internal pressure of the pressurization fluid bag becomes almost equal to the pressure on the artery and thus correct detection of the pressure on the artery is possible.
According to still another aspect of the invention, the press unit of the sphygmomanometer cuff is arranged opposite to the pressurization surface of the pressurization fluid bag and is a fluid bag for press which expands and contracts upon supply and discharge of fluid. The pressurization fluid bag has a restraint tool placed opposite to the pressurization surface for restraining the press fluid bag from swelling in the axial direction of the subject region. When the press fluid bag is expanded, the press fluid bag is prevented by the restraint tool from swelling in the axial direction of the subject region. Therefore, the pressing force generated by expansion of the press fluid bag is efficiently transmitted to the pressurization fluid bag, so that the transmission efficiency of the pressurization force is enhanced.
According to a further aspect of the invention, the pressurization fluid bag of the sphygmomanometer cuff has a pressurization surface which is less elastic than the subject region and has a portion having a compression displacement relative to the pressure from the subject region that is greater than compression displacement of fluid inside the pressurization surface. When pressure is exerted, the pressurization surface is hardly displaced, while the remaining portion is displaced according to the pressurization force. As a result, a uniform distribution of the pressurization force is established over the pressurization surface of the pressurization fluid bag. In other words, the pressurization force is uniform regardless of the position of the pressurization surface, and thus the pressure on the artery can be measured correctly.
According to a further aspect of the invention, the sphygmomanometer cuff includes a cover for preventing the pressurization fluid bag, when the cuff is attached to the subject region, from being subjected to pressure from the subject region or any external pressure. As the pressurization fluid bag is not subjected to the pressure from the subject region or external pressure owing to the cover upon attachment, zero point of the pressure can precisely be adjusted with the cuff attached as it is whereby a correct measurement of the blood pressure is possible.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.